Polyamide hollow fiber for artificial hair, head accessory including same, and method for manufacturing polyamide hollow fiber for artificial hair

ABSTRACT

Provided are an artificial hair fiber having a soft texture and appearance close to human hair, and being light in weight; and a head accessory including the artificial hair fiber. A polyamide fiber for artificial hair includes a resin composition that includes a polyamide resin as a primary component resin, and is a hollow fiber having a void in the cross-sectional center section, the void percentage of the polyamide fiber is 15-40%, the fiber specific gravity of the polyamide fiber is 0.80-1.10, and the bend rigidity of the polyamide fiber is 1.5×10 −3  to 5.5×10 −3  gf·cm 2 /yarn.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority to International Patent Application No. PCT/JP2022/003149, filed Jan. 27, 2022, and to Japanese Patent Application No. 2021-021622, filed Feb. 15, 2021, the entire contents of each are incorporated herein by reference.

BACKGROUND Technical Field

The present disclosure relates to polyamide hollow fibers for use as artificial hair or for use as an alternative to human hair. The present disclosure also relates to head decoration articles including the polyamide hollow fibers and to a method for producing polyamide hollow fibers for use as artificial hair.

Background Art

Traditionally, human hair is used for head decoration articles such as hairpieces, hair wigs, false hair, hair bands, and doll hair. In recent years, however, human hair has increased in price and become harder to obtain, and there has been an increasing demand for artificial hair as an alternative to human hair. Synthetic fibers for artificial hair include acrylic fibers, vinyl chloride fibers, vinylidene chloride fibers, polyester fibers, polyamide fibers, polyolefin fibers, and so on. Artificial hair is required to have a human hair-like feel and appearance, an ability to be combed, an ability to be curled, flame retardancy, and other desirable properties. Particularly in recent years, besides these properties, artificial hair has been required to be lightweight so that it can provide a natural feel when worn. Lightweight fibers for artificial hair are disclosed, for example, including hollow fibers having a flat multilobed cross-section with a bore at its center, as described, for example, in PCT International Publication No. WO2014/196642

SUMMARY

WO2014/196642 discloses polyester and polyamide hollow fibers for artificial hair. Unfortunately, among them, the polyester fibers, although they are lightweight and have a human hair-like appearance, are less likely to have a soft human hair-like feel because of their hollow structure, and it still remains a challenge to simultaneously achieve soft feel and light weight. On the other hand, the polyamide fibers, although they are relatively lightweight thanks to their hollow structure, have room for improvement because they still cannot provide sufficiently lightweight artificial hair, for example, with a void fraction of more than 15%. Thus, there is still a strong need for artificial hair fibers having a soft human hair-like feel and high lightweight properties simultaneously.

As a result of intensive studies, the inventors have created polyamide fibers including a certain polyamide resin composition and having certain levels of void fraction, specific gravity, and bending stiffness and have found that such polyamide fibers are highly lightweight while maintaining a soft human hair-like feel and a human hair-like appearance. Specifically, the present disclosure is directed to a polyamide hollow fiber for use as artificial hair, the fiber including a resin composition that includes a polyamide resin as a main resin component and having a void fraction of 15 to 40%, a specific gravity of 0.80 to 1.10, and a bending stiffness of 1.5×10⁻³ to 5.5×10⁻³ gf·cm²/yarn.

The present disclosure provides artificial hair fibers having a soft human hair-like feel and a human hair-like appearance and being highly lightweight, provides head decoration articles including such artificial hair fibers, and provides a method for producing such artificial hair fibers.

BRIEF DESCRIPTION OF THE DRAWINGS

The FIGURE is a laser micrograph of cross-sections of fibers of Example 1.

DETAILED DESCRIPTION <Fiber Shape>

In one or more embodiments of the present disclosure, the polyamide hollow fiber for use as artificial hair may have a cross-section with an outer shape (the shape of the outer periphery of the fiber) being a circle or any other shape, such as an ellipse, a flat shape, or a flat multilobed shape. For a soft human hair-like feel, a human hair-like appearance, and an ability to be combed, the cross-section preferably has a flat multilobed shape. The flat multilobed shape may be composed of: two or more leaf portions each having at least one shape selected from the group consisting of a circular shape and an elliptical shape; and recessed portions that connect the leaf portions. The circular or elliptical shape does not necessarily have to be a continuous arc and is intended to include a partially deformed circle or ellipse, which is substantially circular or elliptical as long as it is not acutely angled. In this regard, it is also not necessary to take into account irregularities of 2 μm or less formed on the cross-section of the fiber or on the outer periphery of its core portion by addition of an additive or other materials. In particular, the cross-section preferably has a flat bilobed shape composed of: two circular or elliptical portions; and recessed portions connecting the circular or elliptical portions.

In one or more embodiments of the present disclosure, the polyamide hollow fiber for use as artificial hair, which has a void (called a bore), may have a concentric structure in which the center position of the bore is coincident with the center position of the fiber cross-section or may have an eccentric structure in which the center position of the bore is eccentric from (not coincident with) the center position of the fiber cross-section. Preferably, the center position of the bore is coincident with the center position of the fiber cross-section. The cross-sectional shape of the bore may be the same as or different from the outer shape of the fiber. The cross-section of the fiber may or may not have a cross-linked hollow section. In particular, the cross-section of the fiber preferably has a single bore with no cross-linked section. The fiber with such a feature will have a smaller amount of light-reflecting interfaces and a more human hair-like appearance than the fiber with a cross-linked section.

In one or more embodiments of the present disclosure, the shape of the bore is preferably, but not limited to, a polygonal shape having: a first side approximately perpendicular to the long axis of the cross-section of the fiber; and a second side approximately perpendicular to the long axis of the cross-section of the fiber. In the polygonal shape, the first and second sides are preferably approximately parallel to each other. Specifically, to ensure a high void fraction, to disperse the stress at corners, and to reduce surface reflection, the polygonal shape is preferably, for example, tetragonal, pentagonal, hexagonal, heptagonal, or octagonal. When pressure is applied to the fiber, the bore with such a shape can prevent the pressure from being applied to a specific local portion (point) and allow the pressure to be applied to lines (first and second sides) so that the fiber can be protected from deformation and collapse.

In one or more embodiments of the present disclosure, the first and second sides of the bore each preferably have a length of 1 μm or more and 150 μm or less, more preferably a length of 3 μm or more and 140 μm or less. In the present disclosure, the length of the first side of the bore may be defined as the average of bore sides in the cross-sections of any 30 selected fibers. In this regard, the maximum and minimum lengths of the first sides of the bores in the cross-sections of any 30 selected fibers preferably fall within the range specified above. In the present disclosure, the length of the second side of the bore may be defined as the average of bore sides in the cross-sections of any 30 selected fibers. In this regard, the maximum and minimum lengths of the second sides of the bores in the cross-sections of any 30 selected fibers preferably fall within the range specified above. Setting the length of the first and second sides to 1 μm or more will help to prevent local concentration of pressure on the fiber, to provide a good feel to the fiber, and to make the cross-section of the fiber less likely to break or collapse. Setting the length of the first and second sides to 1 μm or more will also help to make the fibers less likely to tangle and allow the fibers to have a good ability to be combed. Setting the length of the first and second sides to 150 μm or less will allow the fiber to have an outer periphery apart from the outer periphery of the bore, to be satisfactorily lightweight and not excessively thin, and to have a cross-section that is less likely to break or collapse. Setting the length of the first and second sides to 150 μm or less will also make the fibers less likely to tangle and allow the fibers to have a good ability to be combed.

In one or more embodiments of the present disclosure, the fiber has a void fraction of 15 to 40%, preferably 15 to 35%, more preferably 18 to 35%, or even more preferably 18 to 30%. Setting the void fraction in such a range allows the fiber to be sufficiently lightweight and makes the fiber less likely to have an extremely thin cross-sectional portion so that the fiber can be spun efficiently. In the present disclosure, the void fraction may be defined as the average of the bore area-to-total cross-sectional area ratios of any 30 selected fibers, in which the cross-sectional area is perpendicular to the longitudinal direction of the fiber. The total cross-sectional area refers to the area surrounded by the outer periphery of the fiber, which covers the area of the bore. In this regard, the maximum and minimum values of the void fractions determined for the cross-sections of any 30 selected fibers each preferably fall within the range specified above. The void fraction can be appropriately adjusted by controlling nozzle shape, nozzle temperature, spinning speed, discharge rate during spinning, quench conditions, draft ratio, draw ratio, resin composition melt viscosity, and other conditions.

In one or more embodiments of the present disclosure, the specific gravity of the fiber is an indicator to measure the lightweight properties. The lower the specific gravity, the higher the lightweight properties. The specific gravity of the fiber may be calculated based on the Archimedes method. The specific gravity of the fiber is 0.80 to 1.10, preferably 0.80 to 1.05, or more preferably 0.85 to 1.05. The fiber with a specific gravity in such a range is sufficiently lightweight and is less likely to have an extremely thin cross-sectional portion so that it can be spun efficiently. The specific gravity of the fiber may be adjusted mainly by changing the void fraction.

In one or more embodiments of the present disclosure, the bending stiffness of the fiber is an indicator to measure the feel of the fiber. The bending stiffness of the fiber is preferably 1.5×10⁻³ to 5.5×10⁻³ gf·cm²/yarn, more preferably 2.0×10⁻³ to 5.5×10⁻³ gf·cm²/yarn, or even more preferably 2.0×10⁻³ to 5.0×10⁻³ gf·cm²/yarn. The fiber with a bending stiffness in such a range will have a highly soft, human hair-like feel. The bending stiffness can be appropriately adjusted by controlling the outer shape of the cross-section of the fiber, the cross-sectional shape of the bore, the void fraction, the single fiber fineness, the conditions for the formulation of the resin composition, the crystallinity of the resin, and other conditions.

In one or more embodiments of the present disclosure, for suitable use as an alternative to human hair, the fiber preferably has a single fiber fineness of 10 dtex or more and 150 dtex or less, more preferably 15 dtex or more and 100 dtex or less, or even more preferably 20 dtex or more and 80 dtex or less. The fiber with a single fiber fineness in such a range will have a human hair-like feel and appearance and can be spun efficiently.

<Resin Composition>

In one or more embodiments of the present disclosure, the artificial hair fiber includes a resin composition that includes a polyamide resin as a main resin component to provide a soft human hair-like feel. As used herein, the term “main resin component” means a resin present at the highest content in the resin composition. The resin composition may include an additional resin in addition to the polyamide resin, which is the main resin component. Examples of the additional resin include polyester resin, modacrylic resin, polycarbonate resin, polyolefin resin, polystyrene resin, and polyphenylene sulfide resin. The content of the polyamide resin (main resin component) in the resin composition is preferably 60 wt % or more, more preferably 70 wt % or more, even more preferably 75 wt % or more, furthermore preferably 80 wt % or more, based on the total resin weight of the resin composition, which corresponds to 100 wt %.

The melt viscosity of the resin composition is preferably, but not limited to, 100 to 700 Pa·s, more preferably 200 to 600 Pa·s, even more preferably 300 to 600 Pa·s, furthermore preferably 350 to 550 Pa·s. The resin composition with a melt viscosity in such a range can form fibers having a cross-section with a hollow shape similar to that of the spinning nozzle, having a higher void fraction, and being more lightweight. Moreover, the resin composition with a melt viscosity in such a range can be stably spun into fibers with less breakage and less unevenness in fineness. As used herein, the term “melt viscosity” refers to the melt viscosity of a sample of the resin composition measured at a temperature of 280° C. and a shear rate of 50 mm/min after dewatering and drying of the sample.

<Polyamide Resin>

In one or more embodiments of the present disclosure, the fiber for use as artificial hair (artificial hair fiber) includes the resin composition including a polyamide resin as a main resin component. The term “polyamide resin” means a product obtained by polymerization of one or more selected from the group consisting of a lactam, an aminocarboxylic acid, a mixture of a dicarboxylic acid and a diamine, a mixture of a dicarboxylic acid derivative and a diamine, and a dicarboxylic acid diamine salt.

Examples of the lactam include, but are not limited to, 2-azetidinone, 2-pyrrolidinone, δ-valerolactam, ε-caprolactam, enantholactam, capryllactam undecalactam, and laurolactam. Among them, ε-caprolactam, undecalactam, and laurolactam are preferred, and ε-caprolactam is particularly preferred. These lactams may be used alone, or a mixture of two or more of these lactams may be used.

Examples of the aminocarboxylic acid include, but are not limited to, 6-aminocaproic acid, 7-aminoheptanoic acid, 8-aminooctanoic acid, 9-aminononanoic acid, 10-aminodecanoic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid. Among them, 6-aminocaproic acid, 11-aminoundecanoic acid, and 12-aminododecanoic acid are preferred, and 6-aminocaproic acid is particularly preferred. These aminocarboxylic acids may be used alone, or a mixture of two or more of these aminocarboxylic acids may be used.

In a case where a mixture of a dicarboxylic acid and a diamine, a mixture of a dicarboxylic acid derivative and a diamine, or a dicarboxylic acid diamine salt is used, examples of the dicarboxylic acid include, but are not limited to, aliphatic dicarboxylic acids, such as oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, brassylic acid, tetradecanedioic acid, pentadecanedioic acid, and octadecanedioic acid; alicyclic dicarboxylic acids, such as cyclohexanedicarboxylic acid; and aromatic dicarboxylic acids, such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalenedicarboxylic acid. Among them, adipic acid, sebacic acid, dodecanedioic acid, terephthalic acid, and isophthalic acid are preferred, and adipic acid, terephthalic acid, and isophthalic acid are particularly preferred. These dicarboxylic acids may be used alone, or a mixture of two or more of these dicarboxylic acids may be used.

In a case where a mixture of a dicarboxylic acid and a diamine, a mixture of a dicarboxylic acid derivative and a diamine, or a dicarboxylic acid diamine salt is used, examples of the diamine include, but are not limited to, aliphatic diamines, such as 1,4-diaminobutane, 1,5-diaminopentane, 1,6-diaminohexane, 2-methyl-1,5-diaminopentane (MDP), 1,7-diaminoheptane, 1,8-diaminooctane, 1,9-diaminononane, 1,10-diaminodecane, 1,11-diaminoundecane, 1,12-diaminododecane, 1,13-diaminotridecane, 1,14-diaminotetradecane, 1,15-diaminopentadecane, 1,16-diaminohexadecane, 1,17-diaminoheptadecane, 1,18-diaminooctadecane, 1,19-diaminononadecane, and 1,20-diaminoeicosane; alicyclic diamines, such as cyclohexanediamine and bis(4-aminohexyl)methane; and aromatic diamines, such as m-xylylenediamine and p-xylylenediamine. Among them, aliphatic diamines are preferred, and hexamethylenediamine is particularly preferred. These diamines may be used alone, or a mixture of two or more of these diamines may be used.

Preferred examples of the polyamide resin (nylon resin) include nylon 6 (hereinafter also referred to as PA6 (polyamide 6)), nylon 66 (hereinafter also referred to as PA66 (polyamide 66)), nylon 11, nylon 12, nylon 6.10, nylon 6.12, nylon 4.10, nylon 46, nylon 6T, nylon 9T, nylon 10T, nylon MXD6, and copolymers of these nylon resins. In particular, for heat resistance and spinnability, the polyamide resin is more preferably composed mainly of at least one selected from the group consisting of nylon 6, nylon 66, nylon 6.10, nylon 6.12, nylon 4.10, and nylon MXD6. In particular, for cost and availability, the polyamide resin is more preferably composed mainly of at least one selected from the group consisting of nylon 6 and nylon 66. The expression “the polyamide resin is composed mainly of at least one selected from the group consisting of nylon 6 and nylon 66” means that the polyamide resin includes 80 mol % or more of nylon 6 and/or nylon 66.

The viscosity of the polyamide resin may be at any level. The polyamide resin preferably has a relative viscosity in sulfuric acid solution of 2.0 or more and 4.0 or less, more preferably 2.5 or more and 3.8 or less, or even more preferably 2.6 or more and 3.6 or less. The polyamide resin with a relative viscosity in such a range can be formed into fibers with a high void fraction without reduction in mechanical strength. Moreover, the polyamide resin with a relative viscosity in such a range exhibits higher resistance to melt dripping during burning and can be easily melted and spun into fibers with higher production efficiency while their fineness can be easily made uniform. As used herein, the term “relative viscosity in sulfuric acid solution” refers to the relative viscosity, measured at 25° C., of a solution of 0.25 g of the polyamide resin in 25 mL of 98% sulfuric acid.

The polyamide resin may be produced, for example, by a polymerization method in which raw materials for the polyamide resin are heated in the presence or absence of a catalyst. Stirring may or may not be carried out during the polymerization, but stirring is preferred to form a homogeneous product. The polymerization temperature may be set to any suitable level depending on the degree of polymerization for the desired polymer, the reaction yield, and the reaction time. For the quality of the final polyamide resin product, a relatively low polymerization temperature is preferred. The rate of reaction may also be any suitable level. The pressure in the reaction system is preferably, but not limited to, a reduced pressure for efficient removal of volatile components out of the system.

If necessary, the polyamide resin may be end-capped with an end-capping agent, such as a carboxylic acid compound or an amine compound. When a monocarboxylic acid or a monoamine is added to end-cap a nylon resin, the resulting nylon resin will have a terminal amino or carboxyl group concentration lower than that of the corresponding non-capped nylon resin. On the other hand, when a dicarboxylic acid or a diamine is used for the end capping, the ratio of the terminal amino group concentration to the terminal carboxyl group concentration will change while the sum of the concentrations of the terminal amino and carboxyl groups will remain unchanged.

The terminal group concentration of the polyamide resin may be any level. Preferably, the polyamide resin has a high terminal amino group concentration for fiber applications requiring high dye-affinity or for resin applications for the design of materials suitable for alloying. On the other hand, the polyamide resin preferably has a low terminal amino group concentration, for example, in a case where it should be prevented from coloration or gelation under long-term aging conditions. Furthermore, the polyamide resin preferably has low concentrations of terminal carboxyl and amino groups in a case where it should be prevented from lactam regeneration during remelting, from oligomer formation-induced fiber breakage during melting and spinning, from mold deposit formation during continuous injection molding, or from the occurrence of die marks during continuous film extrusion. While the terminal group concentration may be controlled depending on the intended use, the concentrations of terminal amino and carboxyl groups are each preferably 1.0×10⁻⁵ to 15.0×10⁻⁵ eq/g, more preferably 2.0×10⁻⁵ to 12.0×10⁻⁵ eq/g, or even more preferably 3.0×10⁻⁵ to 11.0×10⁻⁵ eq/g.

The end-capping agent addition method may include adding the end-capping agent together with raw materials, such as a caprolactam, at the early stage of polymerization, adding the end-capping agent during the course of polymerization, or adding the end-capping agent during the process of passing the nylon resin melt through a vertical stirring thin-film evaporator. The end-capping agent may be added as is or dissolved in a small amount of a solvent before being added.

<Flame Retardant>

The resin composition preferably contains a flame retardant, such as a brominated flame retardant, a phosphorus flame retardant, or a nitrogen-containing flame retardant. For all of flame retardancy and good feel and appearance, the resin composition preferably contains a brominated flame retardant and/or a phosphorus flame retardant. They may also be used in combination with a nitrogen-containing flame retardant.

Examples of the brominated flame retardant include, but are not limited to, brominated epoxy flame retardants; pentabromotoluene, hexabromobenzene, decabromodiphenyl, decabromodiphenyl ether, bis(tribromophenoxy)ethane, tetrabromophthalic anhydride, ethylene bis(tetrabromophthalimide), ethylene bis(pentabromophenyl), octabromotrimethylphenylindane, tris(tribromoneopentyl)phosphate, and other bromine-containing phosphates; brominated polystyrenes; brominated poly(benzyl acrylate); brominated phenoxy resins; brominated polycarbonate oligomers; tetrabromobisphenol A, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(allyl ether), tetrabromobisphenol A-bis(hydroxyethyl ether), and other tetrabromobisphenol A derivatives; tris(tribromophenoxy)triazine and other bromine-containing triazine compounds; and tris(2,3-dibromopropyl)isocyanurate and other bromine-containing isocyanuric acid compounds. Among them, for heat resistance and flame retardancy, brominated epoxy flame retardants are preferred.

A brominated epoxy flame retardant having a terminal epoxy group or a terminal tribromophenol moiety may be used as a raw material. As a non-limiting example, after melting and kneading, such a brominated epoxy flame retardant preferably includes 80 mol % or more of a structural unit of formula (1) below based on the total number of the structural units of formula (1) and structural units resulting from at least partial modification of the structural units of formula (1), which is normalized to 100 mol %. After melting and kneading, the brominated epoxy flame retardant molecule may have an altered terminal structure. For example, the molecular end of the brominated epoxy flame retardant may be replaced by a hydroxyl group, a phosphate group, a phosphonate group, or any group other than the epoxy group or the tribromophenol moiety or may have an ester group bonded to a polyester component.

The brominated epoxy flame retardant may also have an altered structure at a portion other than the molecular end. For example, the brominated epoxy flame retardant may have secondary hydroxyl and epoxy groups bonded together to form a branched structure, or some of the bromine atoms may be eliminated from the structural unit of formula (1) or one or more bromine atoms may be added to the structural unit of formula (1) as long as the bromine content of the brominated epoxy flame retardant molecule is not changed significantly.

For example, the brominated epoxy flame retardant is preferably a brominated epoxy polymer flame retardant, such as one represented by formula (2) below. In formula (2) below, m is 1 to 1000. The brominated epoxy polymer flame retardant, such as one represented by formula (2) below, may be a commercially available product, such as a brominated epoxy flame retardant manufactured by Sakamoto Yakuhin Kogyo Co., Ltd. (SR-T2MP (trade name)).

Examples of the phosphorus flame retardant include red phosphorus, phosphate compounds, condensed phosphate compounds, phosphate amide compounds, organocyclic phosphorus compounds, phosphinic acid metal salts, and polyphosphates. For human hair-like feel and appearance, the phosphorus flame retardant is preferably one or more selected from the group consisting of a condensed phosphate compound and a phosphinic acid metal salt, and for heat resistance, the phosphorus flame retardant is more preferably a phosphinic acid metal salt.

Examples of the condensed phosphate compound include, but are not limited to, 1,3-phenylene bis(diphenyl phosphate), 1,3-phenylene bis(dixylenyl phosphate), bisphenol A bis(diphenyl phosphate), 2,2-bis(chloromethyl)trimethylene bis(bis(2-chloroethyl)phosphate), polyoxyalkylene bisdichloroalkyl phosphate, and aromatic condensed phosphate polymers. To form highly processable or shapable fibers, the condensed phosphate compound is preferably an aromatic condensed phosphate polymer. The aromatic condensed phosphate polymer may also be an aromatic condensed phosphate copolymer including two or more different repeating units.

Examples of the phosphinic acid metal salt include, but are not limited to, aluminum phosphinate, magnesium phosphinate, barium phosphinate, calcium phosphinate, and zinc phosphinate. Among them, zinc phosphinate is preferred because its metal (zinc) can melt and finely and uniformly disperse into the resin at the resin processing temperature so that the resulting artificial hair fibers can maintain good feel, good appearance, and good ability to be combed, in contrast to the salt of non-zinc metal (e.g., aluminum, magnesium, barium, calcium).

The zinc phosphinate may be a compound represented by formula (3) below, which may be, for example, a commercially available product, such as a phosphorus flame retardant manufactured by Clariant Chemicals (EXOLIT OP950 (trade name)).

In the formula, R¹ and R², which may be the same or different, are each a linear or branched alkyl group, a phenyl group, and/or an aryl group, preferably a linear or branched C₁-C₆ alkyl group and/or an aryl group, more preferably methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, and/or phenyl.

Examples of the zinc phosphinate include zinc dimethylphosphinate, zinc methylethylphosphinate, zinc diethylphosphinate, zinc methyl-n-propylphosphinate, zinc ethyl-n-propylphosphinate, zinc methylphenylphosphinate, zinc ethylphenylphosphinate, and zinc diphenylphosphinate, among which one or more selected from the group consisting of zinc dimethylphosphinate, zinc methylethylphosphinate, and zinc diethylphosphinate are preferred, and zinc diethylphosphinate is more preferred.

Examples of the nitrogen-containing flame retardant include melamine, melamine derivatives, triazine compounds, isocyanurate compounds, azoalkane compounds, guanidine compounds, and phosphazene compounds. Examples of the melamine derivatives include melam, melem, melamine cyanurate, melamine oxalate, melamine phthalate, melamine sulfate, and melamine phosphate compounds (e.g., melamine polyphosphate, melamine pyrophosphate, dimelamine phosphate). Among these melamine derivatives, one or more selected from the group consisting of melamine cyanurate and a melamine phosphate compound are preferred for heat resistance and availability.

The resin composition may contain any amount of the flame retardant. For all of flame retardancy and good feel and appearance, the resin composition preferably contains 5 parts by weight or more and 30 parts by weight or less, more preferably 10 parts by weight or more and 30 parts by weight or less, or even more preferably 10 parts by weight or more and 25 parts by weight or less of the flame retardant, based on 100 parts by weight of the main resin component.

<Flame Retardant Aid>

The resin composition may contain any flame retardant aid. For all of flame retardancy and good feel and appearance, the resin composition preferably contains an antimony-based flame retardant aid and/or a zinc-based flame retardant aid. Examples of the antimony-based flame retardant aid include antimony trioxide, antimony tetroxide, antimony pentoxide, sodium antimonate, potassium antimonate, and calcium antimonate. Examples of the zinc-based flame retardant aid include zinc borate, zinc phosphate, zinc stannate, and calcium zinc molybdate. For good effect on feel and flame retardancy improvement, the resin composition more preferably contains one or more selected from the group consisting of antimony trioxide, antimony pentoxide, and sodium antimonate. These compounds may be used alone or, two or more of these compounds may be used in combination.

For all of flame retardancy and good feel and appearance, the amount of the flame retardant aid in the resin composition is preferably, but not limited to, 0.1 parts by weight or more and 5 parts by weight or less, more preferably 0.5 parts by weight or more and 5 parts by weight or less, or even more preferably 1 part by weight or more and 4 parts by weight or less, based on 100 parts by weight of the main resin component.

The flame retardant aid is preferably in the form of particles with an average particle size of 0.1 μm or more and 10 μm or less, more preferably with an average particle size of 0.2 μm or more and 8 μm or less, or even more preferably with an average particle size of 0.5 μm or more and 5 μm or less. The resin composition containing the flame retardant aid with a particle size in such a range can provide, to the fibers, a good feel and a good ability to be combed.

<Stabilizer>

As a non-limiting example, the resin composition in the fiber according to the present disclosure preferably contains a stabilizer for the purpose of providing, to the fiber, resistance to thermal degradation-induced yellowing of the resin, resistance to thermal degradation-induced reduction in fiber physical properties, or resistance to protrusion formation-induced degradation of feel. For example, the stabilizer preferably includes a copper compound, an alkali halide compound, a fatty acid metal salt, an inorganic metal powder (preferably including one or more elements selected from the group consisting of zinc, aluminum, and magnesium), a phosphorus stabilizer, a hindered phenol antioxidant, or a hindered amine stabilizer. The stabilizer may include one of these compounds or a combination of two or more of these compounds.

The stabilizer preferably includes a hindered phenol antioxidant or a hindered amine stabilizer, which is preferably a compound having an amide group in the molecular skeleton. Such a compound will have high compatibility with the polyamide resin and thus can provide, to the fiber, a good feel and appearance and a high ability to be shaped or processed. Examples of the compound having an amide group in the molecular skeleton include, but are not limited to, N,N′-hexamethylene bis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propenamide] (CAS No.: 23128-74-7, product name: IRGANOX 1098) and N,N′-bis(2,2,6,6-tetramethyl-4-piperidinyl)isophthalamide (CAS No.: 42774-15-2, product name: NYLOSTAB S-EED).

The content of the stabilizer in the resin composition is preferably 0.01 parts by weight or more and 5 parts by weight or less, more preferably 0.05 parts by weight or more and 3 parts by weight or less, even more preferably 0.1 parts by weight or more and 1 part by weight or less, based on 100 parts by weight of the main resin component. At a content in such a range, the stabilizer will be sufficiently effective and allow the fiber to maintain a constant feel and appearance.

<Additional Additive>

To have an appearance close to that of human hair, the fiber according to the present disclosure may contain an additional additive including particles of one or more selected from the group consisting of an inorganic material, an organic resin, and a composite of an inorganic material and an organic resin. The resulting fiber containing such particles can have fine surface asperities, reduced plastic-specific gloss, and a human hair-like appearance. The inorganic particles may be, for example, particles of calcium carbonate, calcium phosphate, a composite of calcium carbonate and calcium phosphate, magnesium carbonate, silicon oxide, titanium oxide, aluminum oxide, magnesium oxide, magnesium hydroxide, zinc oxide, talc, kaolin, montmorillonite, bentonite, or mica. The organic resin particles may be, for example, particles of cross-linked acrylic resin, cross-linked nitrile resin, cross-linked polystyrene resin, cross-linked polyester resin, cross-linked polyamide resin, polycarbonate resin, polyarylate resin, polyolefin resin, melamine resin, fluororesin, or silicone resin. For dispersibility in the resin and for human hair-like appearance, the organic resin particles are preferably particles of one or more selected from the group consisting of cross-linked acrylic resin, cross-linked nitrile resin, and cross-linked polyamide resin. The particles of a composite of an inorganic material and an organic resin may be particles of a composite of an inorganic compound and an organic resin, such as particles of a composite of silica and melamine resin. The particles may be surface-treated with a material for enhancing their adhesion to the resin component, such as an epoxy compound, a silane compound, an isocyanate compound, or a titanate compound. The particles may include one of these materials or a combination of two or more of these materials.

The particles preferably have an average particle size of 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 8 μm or less, or even more preferably 0.5 μm or more and 5 μm or less. The particles with an average particle size in such a range will be sufficiently effective in reducing gloss and allow the fibers to maintain a human hair-like feel and a good ability to be combed.

The content of the particles in the resin composition is preferably 0.05 parts by weight or more and 20 parts by weight or less, more preferably 0.1 parts by weight or more and 10 parts by weight or less, or even more preferably 0.1 parts by weight or more and 5 parts by weight or less, based on 100 parts by weight of the main resin component. At a content in such a range, the particles will be sufficiently effective in reducing gloss and allow the fibers to maintain a human hair-like feel and a good ability to be combed.

If necessary, the resin composition may contain various additives, such as a crystal nucleating agent, a dispersing agent, a lubricant, a fluorescent agent, an antistatic agent, and a pigment, as long as the advantageous effects of the present disclosure are not compromised.

<Method for Producing Artificial Hair Fibers>

The artificial hair fibers may be produced by any method capable of producing fibers each having a continuous inner bore extending in the fiber-axis direction. Examples of such a method include a method including passing air through the center of the material using a conjugate nozzle to form a bore; a method including forming a core-shell structure fiber with a central portion made of a soluble composition using a conjugate nozzle and then dissolving the composition of the central portion to form a bore; and a method including extruding the material through multiple holes and then bonding the multiple extruded products together immediately below the holes. Among these methods, the method including extruding the material through multiple holes and then bonding the multiple extruded products together immediately below the holes is preferred for the convenience and productivity of the process. The method including extruding the material through multiple holes and then bonding the multiple extruded products together immediately below the holes may be, for example, a method including: temporarily forming two or more separate fibers using a nozzle with a gridded land; and then thermally fusing the fibers into a hollow product.

The artificial hair fibers according to the present disclosure may be produced, for example, by a process including: melt-kneading the resin composition into pellets; then melting the pellets; and spinning the melt into fibers through a spinneret. During the melt-kneading, the flame retardant, the flame retardant aid, the stabilizer, or any other material may be added to the resin composition as needed. The melt-kneading machine may be, for example, a single screw extruder, a twin screw extruder, a roller, a Banbury mixer, or a kneader. In particular, a twin screw extruder is preferred for control of the degree of kneading and ease of operation.

The resin composition including a polyamide resin as a main resin component may be melted and spun into fibers. In this process, for example, an extruder, a gear pump, a spinneret, and other units may be operated at temperatures of 230° C. or more and 300° C. or less for melting and extrusion, and the spun fibers (undrawn fibers) may be taken up at a speed of 30 m/min or more and 5,000 m/min or less. Specifically, the melting and spinning process may include feeding the resin composition from an extruder to form a polymer melt; and discharging the polymer melt through a spinning nozzle (holes) with a specific shape to form fibers (undrawn fibers). The number of filaments discharged from a single spinning nozzle is preferably, but not limited to, 20 to 300. Setting the number of filaments to less than 20 may result in low productivity, and setting the number of filaments to more than 300 may cause a reduction in cooling efficiency and unevenness of fineness.

The fineness and other properties of the spun fibers can be controlled, for example, by cooling with a cooling water tank or by air blow cooling. The temperature and length of the heating cylinder, the temperature and blowing rate of the cooling air, the temperature of the cooling water tank, the cooling time, and the take-up speed may be appropriately controlled depending on the amount of discharge of the polymer and the number of spinneret holes.

The spun fibers (undrawn fibers) are preferably subjected to drawing. The drawing may be performed by either a two-step method, which includes temporarily taking up the spun fibers and then drawing the fibers, or a direct spinning and drawing method, which includes continuously drawing the spun fibers without taking up them. The drawing may be performed by a single-stage drawing process or a multi-stage drawing process, which includes two or more stages.

The heating means for the drawing may be a heating roller, a heating plate, a steam jet system, a hot water bath, or any combination thereof.

An oil agent, such as a fiber treatment agent or a softening agent, may be applied to the artificial hair fibers to provide a more human-hair like feel and feature to them. Examples of the fiber treatment agent include silicone and non-silicone fiber treatment agents for improving the feel and the ability to be combed.

A dye or colorant may be applied to the artificial hair fibers to control the fiber color as needed.

The artificial hair fibers may be subjected to a gear crimping process. The gear crimping process gently crimps the fibers to provide a natural appearance to the fibers and to reduce attraction between the fibers so that the fibers can have a higher ability to be combed. In general, the gear crimping process may include heating the fibers to at least the softening temperature; and passing the heated fibers between two intermeshing gears to transfer the shape of the gears to the fibers and thus to crimp the fibers.

The artificial hair fibers may be a group of fibers, such as a bundle of fibers, in which not all the fibers necessarily need to have the same level of fineness or the same cross-sectional shape and which may be a mixture of fibers with different levels of fineness or different cross-sectional shapes.

<Head Decoration Article>

The artificial hair fibers may be used for a head decoration article. Examples of the head decoration article include, but are not limited to, hair wigs, hairpieces, hair weaves, hair extensions, braided hair, hair accessories, and doll hair.

The head decoration article may include only the artificial hair fibers according to the present disclosure. Alternatively, the head decoration article may include the artificial hair fibers according to the present disclosure in combination with other artificial hair fibers or natural fibers, such as human or animal hair.

EXAMPLES

Hereinafter, the present disclosure will be described more specifically with reference to examples. It should be noted that the examples are not intended to limit the present disclosure.

The measurement and evaluation methods shown below were used in the examples and the comparative examples.

(Void Fraction)

After a bundle of fibers was inserted in a rubber tube, the tube was cross-sectionally cut with a cutter knife so that a fiber bundle piece was obtained for cross-sectional observation. A fiber cross-section photograph was obtained by photographing the fiber bundle piece with a digital microscope (VHX-6000 manufactured by Keyence Corporation) at a magnification of 500×. From the fiber cross-section photograph, the cross-sections of 30 fibers were selected at random and used to calculate the void fraction using an image analyzer (with image analysis software WinROOF manufactured by Mitani Corporation). The calculated value was the average of the measurements of the 30 fiber cross-sections selected at random.

(Fiber Specific Gravity)

The fiber specific gravity was measured at room temperature as shown below based on the Archimedes method using water medium and an electronic densimeter (MDS-300 manufactured by Alpha Mirage Co., Ltd.). First, fibers were cut into pieces with a length of 5 cm and a weight of approximately 0.5 to 1.0 g, which were bundled together. The fiber bundle was then submerged in water medium and determined for specific gravity. When the fibers had a specific gravity lower than that of water, the fiber bundle was fixed in water using the accompanying angle during the measurement.

(Bending Stiffness)

A KES-FB2 pure bending tester (manufactured by Kato Tech Co., Ltd.) was used to measure bending stiffness as shown below. First, 49 fibers (monofilaments) were bonded at intervals of 1 mm to a mount, and the top and bottom of the bonded fibers were fixed with cellophane tapes for preventing slack. The resulting sample was fixed to the jig of the tester and subjected to measurement at room temperature, normal humidity, a deformation rate of 0.5 cm/sec, and a curvature in the range of −2.5 to +2.5 (cm⁻¹). The average of repulsive forces between the curvatures 0.5 and 1.5 (cm⁻¹) was determined and used to calculate the bending stiffness value per fiber.

(Single Fiber Fineness)

An automatic vibroscope fineness meter (DENIER COMPUTER DC-11 manufactured by Search Co., Ltd.) was used to measure 30 sample fibers. The average of the 30 measurements was calculated and used as the single fiber fineness.

(Soft Feel)

Professional hairstylists carried out a sensory evaluation based on the four criteria below.

-   -   A: The fibers have a highly-soft and good human hair-like feel.     -   B: The fibers have a soft and good feel although their feel is         slightly inferior to that of human hair.     -   C: The fibers have a hard feel, and their feel is interior to         that of human hair.     -   D: The fibers have a hard feel, and their feel is much inferior         to that of human hair.

(Lightweight Properties)

The lightweight properties of fibers were evaluated based on the four criteria below using the fiber specific gravity measured and calculated by the method described above.

-   -   A: The fiber specific gravity is 1.00 or less.     -   B: The fiber specific gravity is 1.01 to 1.10.     -   C: The fiber specific gravity is 1.11 to 1.20.     -   D: The fiber specific gravity is more than 1.20.

(Gloss)

The gloss of fibers was evaluated by a visual sensory test based on the four criteria below.

-   -   A: The fibers have a more sufficiently low level of gloss, which         is very close to that of human hair.     -   B: The fibers have a sufficiently low level of gloss, which is         close to that of human hair.     -   C: The fibers have an insufficiently low level of gloss or an         extremely low level of gloss, which is different from that of         human hair.     -   D: The fibers have a certain level of gloss (not reduced) or an         extremely low level of gloss, which is much different from that         of human hair.

(Ability to Be Combed)

While uncurled completely, the fibers were cut into 70 cm-long pieces, and 25 g of the resulting 70 cm-long pieces were bundled. A string was then tied at the center of the fiber bundle. The fiber bundle was then folded in half with the string fixed, so that the fiber bundle was made ready for hair ironing. Next, the fiber bundle was heated with a hair iron (Izunami ITC 450 Flat Iron manufactured by Izunami Inc.) at 180° C., during which the heated hair iron being pressed against the fiber bundle was moved five times from the bottom, at which the fiber bundle was fixed, to the top of the fibers, so that the fiber bundle was made ready for evaluation of its ability to be combed. Subsequently, the fiber bundle for evaluation was combed 100 times from the bottom, at which the fiber bundle was fixed, to the top of the fibers using a hair comb (Matador Professional 386.8 1/2F made in Germany), and then the number of deformed, broken, or cleaved fibers was counted for the evaluation of its ability to be combed based on the criteria below.

-   -   Level A: After the 100 times combing, the number of deformed or         cleaved fibers is less than 10, and smooth combing is possible         all the way.     -   Level B: After the 100 times combing, the number of deformed or         cleaved fibers is 10 or more and less than 30, and combing is         possible all the way although resistance to combing slightly         increases during the course of the 100 times combing.     -   Level C: After the 100 times combing, the number of deformed or         cleaved fibers is 30 or more and less than 100, and resistance         to combing increases during the course of the 100 times combing         and combing incompletion occurs at a frequency of 1 or more and         less than 20 in 100.     -   Level D: After the 100 times combing, the number of deformed or         cleaved fibers is 100 or more, and resistance to combing         increases during the course of the 100 times combing and combing         incompletion occurs at a frequency of 20 or more in 100.

Example 1

Nylon 6 (A1030BRF (trade name) manufactured by Unitika Ltd.) was dried at 70° C. overnight. To 100 parts by weight of the dried nylon 6 were added 15 parts by weight of a brominated epoxy flame retardant (SR-T2MP (trade name) manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.), 2 parts by weight of sodium antimonate (SA-A (trade name) manufactured by Nihon Seiko Co., Ltd.) (a flame retardant aid), and 0.75 parts by weight of a stabilizer (NYLOSTAB S-EED (trade name) manufactured by Clariant Chemicals). The mixture was dry blended and then fed to a twin screw extruder, with which the dry blend was melted and kneaded at a set temperature of 260° C. and formed into resin composition pellets. The resulting pellets were dried at 70° C. overnight. Next, the dried pellets were fed to an extruder, and the resulting melt was extruded through a spinneret (with 120 holes) at a set temperature of 260° C. The resulting fibers were taken up at a speed of 100 m/min to give undrawn fibers. The resulting fibers were hollow fibers each having a bore, which were formed using a process including: temporarily forming two or more separate fibers using a nozzle with a gridded land; and then thermally fusing the fibers into a hollow product.

The resulting undrawn fibers were drawn to three times the length using a heating roll at 110° C. The drawn fibers were then continuously heat-treated using a heating roll at 200° C., then coated with a processing oil agent, and then dried to give polyamide fibers each having a flat bilobed cross-section and a rectangular bore (see the FIGURE). The resulting fibers had a single fiber fineness of 56 dtex.

Example 2

In Example 2, fibers were produced under the same conditions as those in Example 1 except that the set temperature of the spinneret was 245° C. The resulting fibers had a single fiber fineness of 56 dtex.

Example 3

In Example 3, fibers were produced under the same conditions as those in Example 2 except that the take-up speed was 105 m/min during the spinning. The resulting fibers had a single fiber fineness of 53 dtex.

Example 4

In Example 4, fibers were produced under the same conditions as those in Example 2 except that the take-up speed was 110 m/min during the spinning. The resulting fibers had a single fiber fineness of 49 dtex.

Comparative Example 1

In Comparative Example 1, fibers were produced under the same conditions as those in Example 1 except that the shape of the nozzle hole was changed. The resulting fibers had a single fiber fineness of 55 dtex.

Comparative Example 2

In Comparative Example 2, fibers were produced under the same conditions as those in Example 1 except that a nozzle for forming non-hollow fibers was used instead. The resulting fibers had a single fiber fineness of 68 dtex.

Comparative Example 3

Polyethylene terephthalate (A-12 (trade name) manufactured by East West Chemical Private Limited) was dried at 120° C. overnight. To 100 parts by weight of the dried polyethylene terephthalate were added 20 parts by weight of a brominated epoxy flame retardant (SR-T2MP (trade name) manufactured by Sakamoto Yakuhin Kogyo Co., Ltd.) and 2 parts by weight of sodium antimonate (SA-A (trade name) manufactured by Nihon Seiko Co., Ltd.). The mixture was dry blended and then fed to a twin screw extruder, with which the dry blend was melted and kneaded at a set temperature of 275° C. and formed into resin composition pellets. The resulting pellets were dried at 120° C. overnight. Next, the dried pellets were fed to an extruder, and the resulting melt was extruded through a spinneret (with 120 holes) at a set temperature of 260° C. The resulting fibers were taken up at a speed of 100 m/min to give undrawn fibers. The resulting fibers were hollow fibers each having a bore, which were formed using a process including: temporarily forming two or more separate fibers using a nozzle with a gridded land; and then thermally fusing the fibers into a hollow product.

The resulting undrawn fibers were drawn to three times the length using a heating roll at 85° C. The drawn fibers were then continuously heat-treated using a heating roll at 205° C., then coated with a processing oil agent, and then dried to give polyester fibers each having a bore. The resulting fibers had a single fiber fineness of 59 dtex.

Comparative Example 4

In Comparative Example 4, fibers were produced under the same conditions as those in Comparative Example 3 except that a nozzle for forming non-hollow fibers was used instead. The resulting fibers had a single fiber fineness of 63 dtex.

The artificial hair fibers obtained in the examples and the comparative examples were evaluated as described above for soft feel, lightweight properties, gloss, and ability to be combed. The results are shown in Table 1 below.

TABLE 1 Comparative Comparative Comparative Comparative Example1 Example2 Example3 Example4 Example1 Example2 Example3 Example4 Fiber Main resin Polyamide Polyamide Polyamide Polyamide Polyamide Polyamide Polyester Polyester specifications component Fiber outer Flat bilobed Flat bilobed Flat bilobed Flat bilobed Flat bilobed Flat bilobed Flat bilobed Flat bilobed shape Bore shape Rectangular Rectangular Rectangular Rectangular Rectangular (Not hollow) Rectangular (Not hollow) Void 20 22 22 21 12 — 20 — fraction (%) Fiber specific 1.01 0.94 0.95 0.95 1.15 1.23 1.15 1.44 gravity Bending 4.5 4.7 3.2 2.2 3.0 5.3 8.0 7.2 stiffness (10⁻³ gf · cm²/yarn) Artificial Soft feel A A A A A A C C hair fibers Lightweight B A A A C D C D properties Gloss A A A A A A A A Ability to A A A B A B A B be combed

The FIGURE is a laser micrograph of the cross-sections of the fibers of Example 1. The FIGURE shows that the artificial hair fibers each have a flat bilobed cross-section and a rectangular bore.

As shown in Table 1, the polyamide hollow fibers for artificial hair obtained in Example 1 have a relatively high void fraction, good lightweight properties, and a soft human hair-like feel. The polyamide hollow fibers for artificial hair obtained in each of Examples 2, 3, and 4 have a sufficiently high void fraction, very good lightweight properties, and a soft human hair-like feel. The polyamide hollow fibers for artificial hair obtained in Comparative Example 1 have a low void fraction and poor lightweight properties although they have a soft human hair-like feel. The polyamide fibers for artificial hair obtained in Comparative Example 2 are not hollow and have poor lightweight properties although they have a soft human hair-like feel. The polyester hollow fibers for artificial hair obtained in Comparative Example 3 have poor lightweight properties and a feel different from any soft human hair-like feel. The polyester fibers for artificial hair obtained in Comparative Example 4 have very poor lightweight properties and a feel different from any soft human hair-like feel. 

1. A polyamide hollow fiber for use as artificial hair, the fiber having a bore, the bore having a polygonal shape that includes a first side approximately perpendicular to the long axis of the cross-section of the fiber; and a second side approximately perpendicular to the long axis of the cross-section of the fiber, the fiber comprised of a resin composition comprising a polyamide resin as a main resin component, wherein a void fraction of the fiber is from 15 to 40%, a specific gravity of the fiber is from 0.80 to 1.10, and a bending stiffness of the fiber is from 1.5×10⁻³ to 5.5×10⁻³ gf·cm²/yarn.
 2. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the resin composition comprises 100 parts by weight of the main resin component, 5 to 30 parts by weight of a flame retardant, and 0.1 to 5 parts by weight of a flame retardant aid.
 3. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the resin composition comprises at least one polyamide resin selected from the group consisting of polyamide 6 and polyamide
 66. 4. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the resin composition contains at least one flame retardant selected from the group consisting of a brominated flame retardant and a phosphorus flame retardant.
 5. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the resin composition contains at least one flame retardant aid selected from the group consisting of an antimony-based flame retardant aid and a zinc-based flame retardant aid.
 6. A head decoration article comprising the polyamide hollow fiber according to claim
 1. 7. The head decoration article according to claim 6, wherein the head decoration article is one selected from the group consisting of a hair wig, a hairpiece, a hair weave, a hair extension, braided hair, a hair accessory, and doll hair.
 8. A method for producing the polyamide hollow fiber for use as artificial hair according to claim 1, the method comprising melting and spinning a resin composition using a hollow fiber-forming nozzle, wherein the resin composition comprises a polyamide resin as a main resin component.
 9. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the polygonal shape is tetragonal, pentagonal, hexagonal, heptagonal, or octagonal.
 10. The polyamide hollow fiber for use as artificial hair according to claim 1, wherein the fiber has a cross-section with an outer shape, and wherein the cross-section with the outer shape is a flat multilobed shape. 